GB779654A - Improvements in or relating to electric automatic control systems - Google Patents

Abstract

779,654. Automatic control systems. TINSLEY (INDUSTRIAL INSTRUMENTS), Ltd., STEGHART, F. L. F., and CAWTHORNE, C. W. March 24, 1955 [April 7, 1954], No. 10253/54. Class 38 (4). In a system for controlling a variable such as temperature, pressure, &c., an electronic measuring device has its output, depending on the deviation of the variable from a datum value with added integral and differential components, applied to an electromagnetic device 4, Fig. 1, actuating a pivoted jet pipe 6 against the action of a spring 8. The jet pipe is supplied from a fluid pressure source and its nozzle distributes the pressure to a pair of orifices in a distributer 10 for varying the pressures applied through pipes 11, 11a to either side of a piston 12 connected to a valve or other means for controlling the variable. The movement of the pipe from a symmetrical datum position set by a given controller output results in a pressure differential across the piston, so that the latter is displaced to reset the control valve. The piston displacement also results in the actuation of a feed-back linkage 14, 15 to vary the loading of spring 8 in a sense as to restore the jet pipe 6 to its datum position. The piston thus remains in its new position, having undergone a displacement proportional to the controller output and hence to the deviation of the variable plus its integral and differential components. In the electronic measuring device, Fig. 2, a signal representing the variable is applied to terminals 16 for comparison with a reference set on a potentiometer 20, the'resulting error signal flowing in the coil 21 of a galvanometer device 22. The resulting movement of the latter causes the movement of shutters 23, whereby photo-cells 24, 25 are unequally illuminated to cause a change in anode current of valve 27. This current is opposed by a steady current provided by rectifier 28 and the net current, of sense and magnitude representing the deviation of the variable, flows in winding 30 of device 22 in opposition to winding 21, whereby to rebalance the device in its original symmetrical position. The adjustment of a tapping on a resistor 31 varies the proportional band of the whole device. The proportional error current flows in a galvanometer device 32 whose resulting movement causes unequal illumination of photo-cells 35, 36, whereby the charge on condenser 37 is proportional to the integral of the proportional error current. The latter also flows in a resistor 39, whereby the voltage across a resistor 41 of differentiating network 40, 41 is proportional to the first derivative of the proportional error current. The voltages across elements 37, 41 are applied in series to the grid of valve 42, whose output is applied in series with the proportional error current to output terminals 43.